A N
A S S E S S M E N T
O F
T H E C O N V E N T I O N A L

GLOBAL WARMING NARRATIVE

Richard Lindzen
With a comment by Nic Lewis

The Global Warming Policy Foundation
Technical paper 5

An Assessment of the Conventional Global Warming Narrative
Richard Lindzen
Technical paper 5, The Global Warming Policy Foundation© Copyright 2022, The Global Warming Policy Foundation

Contents
About the author	iii

Abstract	

1

1. The popular narrative	

3

2. What is the Earth’s temperature?	

5

3. What is the Earth’s climate?	8

4. What determines the tropics-pole temperature difference?	

10

5. What produces the stability of the tropical temperature?	

11

6. Where does CO₂ fit in the climate?	12

7. Impacts	

12

8. Where does this leave us?	

13

Acknowledgements	

14

References	

15

Comment from Nic Lewis	

17

Response by Richard Lindzen	

20

About the Global Warming Policy Foundation	

23

About the author
Richard S. Lindzen is Alfred P. Sloan Professor of Atmospheric Sciences, Emeritus at the Massachusetts Institute of Technology.

iii

Abstract
The one-dimensional picture of the greenhouse effect and therole of carbon dioxide in this mechanism dominates current depictions of climate and global warming. We briefly review this picture. We then discuss the shortcomings of this approach in dealing with the three-dimensional climate system. One problem isdetermining what temperature on the real Earth corresponds tothe temperature in the one-dimensional treatment. This, in turn,leads to the traditional recognition that the Earth has, in fact,many climate regimes at present. Moreover, there have been profound changes in the temperature difference between the tropics
and polar regions over millennia, but at the same time the temperature of the tropical regions has remained little changed. The
popular narrative assumes that small changes in the tropics areamplified at high latitudes. There is no basis for this assumption.
Rather, the difference is determined by dynamic heat fluxes in theatmosphere and oceans, with the controlling flux due to baroclinic instability in the atmosphere. Changes in mean temperature
are primarily due to changes in the tropic-to-pole difference, andnot to changes in the greenhouse effect. The stability of tropicaltemperatures in the face of strongly varying heat fluxes out fromthose latitudes points to the existence of strong negative feedbacks in the radiative-convective response of the tropics. Finally,
we will comment on the so-called impacts of climate change.

12

1. The popular narrative
We will begin with a brief description of the greenhouse effect ascommonly presented in popular books on climate change (Emanuel 2018, Krauss 2021, for example). Figure 1 is the type of picture that is presented to describe the relevant energy balance fora planet.
Figure 1: Radiativebalance for ahypothetical planet.

Emitted infrared
radiation

Incident solar radiation

PlanetSun

Reflected light
Characteristic
emission level

Although the planet and the sun look spherical, the numbers represent some sort of average, which will, in fact, be applied to a one-dimensional picture. Thus, the net incoming solar
radiation (incident less reflected) must be balanced by the planet’s emitted infrared radiation. Because of the high temperatureof the sun, its radiation is primarily in the visible part of the spectrum. The Earth’s much lower temperature causes its radiation
to be concentrated in the infrared. Because of the presence ofstrong infrared absorbing components in the Earth’s atmosphere(mostly water vapour and clouds, with small contributions from
CO₂, ozone and still more minor constituents), emissions cannot
escape the atmosphere until one gets to a level above which
there is so little absorption as to permit the radiation to escapeto space. This level is referred to as the ‘characteristic emission
level’. The characteristic emission level plays a crucial role in thegreenhouse effect. Balance is achieved when the temperature at
the characteristic emission level is 255 Kelvin (K).
In order to obtain greenhouse warming, one must consider
one more process, namely thermal convection. Radiation alone
leads to convective instability; the surface becomes sufficiently
warmer than the air above it as to lead to convection, which penetrates deep into the atmosphere. Convection in a gas subject
to gravity leads to the temperature decreasing at an adiabatic
lapse rate. For a dry atmosphere, this is given by g/cp (where gis the acceleration of gravity and cp is the heat capacity of dry
air at constant pressure; the result is approximately 9.8 K/km); fora moist atmosphere, where condensation accompanies cooling,
the situation is more complex, but the associated lapse rate isapproximately 6.5 K/km. A review of radiative-convective equilibrium may be found in Goody and Yung (1989). Adding an infrared absorbing gas (i.e. a greenhouse gas) elevates the characteristic emission level and, because of convection, this level is3

colder than 255K. In order to reestablish equilibrium with net incoming radiation, it must be warmed back to 255 K, thus raising
the temperature of the entire atmosphere below this level. Thisis the essence of the so-called greenhouse effect. It is illustrated
in Figure 2.
Figure 2: One-dimensional
greenhouse effect.

Elevated emission level

Altitude Z

Characteristic emission level

255 K

Temperature T

While the effect is commonly attributed to Arrhenius andeven Fourier, this is inaccurate. Those earlier scientists recognisedthat certain gases absorb thermal radiation, but they did not understand the role of convection.
The one-dimensional approach does provide some insights
into the gross differences among the various planets in our solar
system, and it should be noted that almost all current discussionsof global warming are based on one-dimensional approach,largely because of its simplicity. However, as we will see, it is fundamentally inadequate for describing the Earth’s complex threedimensional nature.
Briefly, one begins with an atmosphere that has a preindustrial value for CO₂, and asks how much warming will be associated with a doubling of that concentration. It turns out that thewarming is logarithmic in CO₂ (because the absorption bands of
CO₂ are almost saturated, and absorption is associated with line
wings), so that each doubling is associated with the same warming. The contribution is about 3.5 W/m2, or of the order of 2% of
the normal flux, and leads to warming of about 1°C.
This result is not considered controversial. Normally, one
might consider 2% to be small, since common fluctuations – inupper-level cirrus, low-level clouds, ocean currents, and so on –routinely produce this level of variability in the radiative budget.
In other words, consistent with Le Chatelier’s Principle, the climate
system is amply capable of opposing such forcing. Although thegross inadequacy of our understanding of clouds and other factors is openly acknowledged by the IPCC, concerns over global
4

warming are based on what is essentially the assumption thatvariations in water vapor, clouds, and so on act to amplify rather
than oppose the impact of CO₂; in other words, they are assumed
to be positive rather than negative feedbacks. It is on the egregiousness of these assumptions rather than on the greenhouse effect itself, that most sceptics (including myself) have focused.
As we have just seen, the focus on the one-dimensional viewis understandable. Its particular appeal is to physicists and astrophysicists, since it involves a minimum of detail, while letting
them feel that they have mastered the subject. My point here
is to simply note that these individuals are often deeply familiar
with radiative transfer, but not with fluid dynamics. It was also
taken seriously by many of us who should have known better.
The reason for this was that even this coarse approach required
highly dubious properties for feedbacks and involved insufficiently accurate radiative transfer calculations. In brief, even thisoversimplified approach demanded better assessment.
Although the exposition above is the conventional explanation of the greenhouse effect, most projections refer to largescale models of the atmosphere known as GCMs. The original
expansion of this abbreviation was ‘general circulation model.’However, increasingly, they seem to be referred to as ‘global climate models.’ These models do include much of the complexityof the real atmosphere, but they cannot provide the spatial resolution to handle processes such as vertical convection (that is, cumulonimbus towers), clouds in general and turbulence, which, asa result, require the use of questionable parameterisations. Theydo, however, permit the inclusion of arbitrary feedbacks, whichenable models to produce a wide variety of results. Nevertheless,even these models do not predict catastrophic changes due toincreasing CO₂. Moreover, they do not adequately describe eventhe present climate (Boyle, 2006). They do especially poorly atrepresenting the natural internal variability of the atmosphereand the oceans, and almost all of them fail to correctly anticipatechanges in the commonly used measure of global temperature.
Nor do they simulate past climates adequately. This has been
openly acknowledged by some of the modelers who have been
most supportive of the global warming narrative (Hausfather etal., 2022).
Virtually all critiques of the global warming issue have focused on feedbacks, the inadequacies of the models, and one
other matter: the claims of various things having changed (socalled ‘impacts’). I will briefly return to this other matter later.

2. What is the Earth’s temperature?
One characteristic of current discussions of climate is the focus
on the temperature of the Earth. While this is clear in the one-dimensional picture, the Earth is not one-dimensional, and the notion of the Earth’s temperature is, itself, a problematic and highly
misleading metric.
5Clearly, it is not the average temperature. After all, what doesit mean to average Mount Everest with the Dead Sea? What isused instead is the average anomaly (defined as the deviationfrom 30-year means at each station). This anomaly is actually
the small residue of widely spread dense data points. These data
points are shown in Figure 3, an update by Lindzen and Christy(2020) of work originally done by the late Stanley Grotch at theLawrence Livermore Laboratory. Note the temperature scale. It
extends over a range of almost 20°C!

The Berkeley Earth Surface
Temperature Data (BEST) wasused because it was conveniently
available.

12
Temperature anomaly (°C)

Figure 3: Seasonaltemperature anomalies
at individual stations.

8
4
0
-4
-8
-12
1900

1920

1940

1960

1980

2000

Figure 4 shows both the average and the data points. The average is shown by yellow points with orange boundaries. At any
particular time, almost as many stations will be cooling as warming because the anomaly is so small.
12
Temperature anomaly (°C)

Figure 4: Same as Figure 3,
but with average shown.

8
4
0
-4
-8
-12
1900

1920

1940

1960

1980

2000

In order to disguise this, one presents the average without
the data points and expands the temperature scale by about anorder of magnitude. The result is shown in Figure 5.
Blowing up the scale and omitting the data points serves to6

1.2

Figure 5: Averagetemperature anomaly
without the data points.

Temperature anomaly (°C)

0.8

0.4

0

-0.4

-0.8
1900

1920

1940

1960

1980

2000

disguise the fact that we are still talking about really small temperature changes. Although we are told that increases of another 0.5°C represent catastrophe, it pays to put such changes into
perspective. This is done in Figure 6, where we show the smallchanges in the mean compared to changes that we routinely
deal with.
80

Degrees centigrade

60

40

20

0

Global warming
last 120 years
DenverKansas City
Chicago8am–
10am

Sunrise–afternoon
Nashville
New York City
BostonJan avg–
Jul avg
Atlanta
Phoenix
SeattleJan morning– Ann. average
RecordJul afternoon coldest–hottest coldest–hottest
DallasMiami
New Orleans
AverageLos Angeles

Figure 6: Various temperature changes that people and the rest of nature already deal with.
7

It may be worth noting that the Working Group I report (thepart dealing with the science) of the UN’s Intergovernmental
Panel on Climate Change never suggests that 0.5°C of additional
warming represents an existential threat. Indeed, it doesn’t suggest existential threats at all. Where in the world do such claims
come from? It seems that despite decades of claims of the certainties around the (at least) public and public policy climate
narrative, policy actions haven’t been aggressive enough for
proponents of the crisis-demands-action camp, and thus there’s
been an escalation of hyperbole about an imminent apocalypse.
Needless to add, this has not served constructively in clarifying
the underlying realities of climate science.

3. What is the Earth’s climate?
It should be recognised that climate science, prior to about 1980,
was a very small field. Indeed, at MIT in 1990, no-one working on
climate-related aspects of meteorology, oceanography, marine
geochemistry, geology, and so on referred to themselves as climate scientists (although today, all of them do). Indeed, until the
1970s, the meteorological literature on climate didn’t emphasise,or even mention, the greenhouse effect (Climatology, Haurwitz

Figure 7: World map showing climatic regimes
following the Köppen classification.
8and Austin, 1944, Climate, Pfeffer, 1960, Atmosphere, Weather andClimate, Barry and Chorley, 1970). Instead, they were concernedwith understanding the wide variety of climate regimes thatwere found at the time (and, for that matter, still are). These arecommonly described by the Köppen classification, as shown in
Figure 7.
Much of the explanation for these regimes consists of largely ‘just so’ stories, but that isn’t unusual in the earth sciences. The
approach of theoreticians like myself tends to be more mathematical and focused. We try to isolate features like the Hadley circulations and stationary waves. Oceanographers have their own
pet features. Milankovitch insightfully identified orbital variations in producing cycles of glaciation – something substantiallycorroborated in more recent papers (Roe, 2006, Edvardsson et al,2002). Interestingly, none of the approaches is so naïve as to assume that there is some mean ‘temperature’ that determines thenumerous features of the Köppen picture – as well as a single
primary cause, such as CO₂.
In considering climate change, the Soviet climatologists Budyko and Izrael (1991) noted that it mostly manifested as changes
in the tropics-to-pole temperature difference; tropical temperatures changed very little. The change in the mean temperature isalmost entirely due to changes in the tropics-Arctic temperature
difference. This is illustrated more explicitly in Figure 8.

Figure 8: Simplified pictureof meridional temperature
distribution between
the Equator (sinϕ = 0)
and the Pole (sinϕ = 1)

T

T₁
T₂

sinϕ = 0
Equatorx₁

ΔT = ΔT₁ −Δ(δT₂)

1−x₁
2

δT₂

sinϕ = 1
Pole

Note that if ΔT₁ is small, ΔT will be dominated by Δ(δT₂). For
major climate changes, this has been the case. The crucial pointis that Δ(δT₂) is not a response to ΔT₁; in other words, it is not
an amplification of whatever is happening in the tropics. It is ofcourse possible, during periods when Δ(δT₂) is small, that ΔT will
be dominated by ΔT₁, but these periods will not represent major
climate change.
By the 1980s, with advances in paleoclimatology, several
aspects of climate history emerged with increased clarity. We
9began to see more clearly the cyclic nature of glaciations of thepast million years or so (Imbrie and Imbrie, 1979). Warm periods,
such as the Eocene (50 million years ago), became better defined(Shackleton and Boersma, 1981). The data suggested that for
both glacial periods and the warm periods, equatorial temperatures did not differ much from present values, but the temperature difference between the tropics and high latitudes varied
greatly (Table 1).
Table 1: Temperature
difference between tropics
and high latitudes.

PeriodEoceneGlacial maximumToday

ΔT (°C)
≈20
≈60
≈40

The variations in equatorial temperatures were much smaller.

4. What determines the tropics-pole temperature difference?
Adherents of today’s popular narrative invoke an imaginary ‘polar
amplification’, which some models (to their credit) fail to display(Lee, et al, 2008). However, the physical basis for this difference is,in fact, well known. It is driven by the heat flux from the tropics
to the polar region. There are heat fluxes associated with ocean
currents and a number of atmospheric processes. However, thecontrolling heat flux is primarily due to convection, associatedwith what are called baroclinic instabilities (Pedlosky (1992), Holton and Hakim (2012), Lindzen (1990), or virtually any textbook
on geophysical fluid dynamics).
These instabilities are ‘controlling’ because they work tobring about the temperature distribution that neutralises the instability (Lindzen, 2020, Lindzen and Farrell, 1980). The fact thatsome of the transport is due to other processes, such as oceanic transport and stationary waves, simply removes the need fortransport by baroclinic instability. However, heat transport by baroclinic instabilities will contribute whatever more is needed toachieve baroclinic neutrality.1
A better-known example of controlling instabilities is vertical convection due to heating from below. In a laboratory-scale
incompressible liquid, convective instability arises from temper1 However, for readers who want a quick description, the following shortvideo ‘DIYnamics: Baroclinic eddies in a tank and in Earth’s atmosphere‘, provides a sense of how baroclinic instabilities emerge in a rotating tank driven
by heat flux from a warm edge to cold center. https://youtu.be/5bnmaYOFe
rk?list=TLPQMzAwMTIwMjJrK1Y3llvMXA. The video ends by stating, ‘Changes in overall temperature contrast affect the behavior of eddies … so climatechange may alter Earth’s eddies, and the weather they produce‘. It should be
noted that in a warmer world, this difference is expected to decrease.

10

ature decreasing with height – warmer liquid being more buoyant. The convection acts to eliminate the vertical gradient of temperature. The situation is more complicated for a compressible
gas. Convection leads to a moist adiabatic lapse rate (i.e. the rate
at which temperature decreases with height) for the tropical atmosphere. Radiative-convective equilibrium is largely restricted
to the tropics. The stability of the tropical temperature suggests
negative rather than positive feedbacks, since the tropical temperatures remain relatively stable despite the varying heat fluxes
from the tropics.
An important question is, why does the climate have different tropics-polar temperature differences? Results of theoreticalstudies show that equilibration only determines the temperature
difference at the level of the Arctic tropopause around 6 km (Jansen and Ferrari, 2013). This is, in fact, observed to be about 20°C
(viz Newell et al.,1972), which is the difference that characterises
the Eocene. The differences at the surface seem to be associatedwith the existence of Arctic inversions, which are in turn associated with the presence of ice and snow, but are currently not fully
understood. To be sure, changes in greenhouse forcing may playsome role, but with respect to the glaciation cycles, changes due
to orbital variations provide changes in insolation of the order of
100 W/m2 in the Arctic in summer, which is the relevant factor in
the Milankovitch theory (Roe, 2006), while changes in CO₂ contribute about 1.5 W/m2.
Assuming that changes in the mean due to changes in thetropics-to-pole temperature difference result from the role of
CO₂ in the greenhouse effect makes no sense. It is, in some ways,
a confusion of cause with effect.

5. What produces the stability of the tropicaltemperature?
As already noted, the relative stability of tropical temperatures
is suggestive of negative feedbacks, and there are many ways inwhich these might arise. Their representation as positive feedbacks in GCMs has little actual basis in observation or theory,
despite modellers‘ energetic searches for evidence to support
the idea. One negative feedback for which there is substantial
evidence is the so-called iris effect, wherein upper-level thin cirrus clouds (which are powerful greenhouse substances) reduce
their coverage as surface temperature increases (Lindzen, Chouand Hou, 2000, Lindzen and Choi, 2021 and references therein).
This mechanism is potentially strong enough to account for the
Early Faint Sun Paradox (Sagan and Mullen,1972, Rondanelli and
Lindzen, 2007). This paradox refers the Earth of 2.5 billion years
ago, when solar output was 30% less than today. However, despite this, observations suggest the Earth remained close to thepresent climate, with no evidence of ice. Recall that doubling CO₂
only produces a 2% perturbation to the radiative budget.
11

6. Where does CO₂ fit in the climate?
What should be clear is that it is absurd to assume that the complex three-dimensional climate is defined by the small difference of large numbers that is the average temperature anomaly,
and that the controlling factor is the small contribution of CO₂.
The Earth’s climate has, indeed, undergone major variations, butthese offer no evidence of a causal role for CO₂. For the glaciation
cycles of the past 700 thousand years, the proxy data from the
Vostok ice cores shows that cooling precedes decreases in CO₂
despite the very coarse temporal resolution (Jouzel et al.,1987,
Gore, 2006). Higher temporal resolution is needed to show thatwarming preceded the increase in CO₂ as well (Caillon et al, 2003).
For earlier variations, there is no suggestion of any correlation
with carbon dioxide at all, as shown in Figure 9a, a commonly
presented reconstruction of CO₂ levels and ‘temperature’ for the
past 600 million years or so.
To be sure, paleoclimatological reconstructions are somewhat speculative – especially as concerns CO₂, but a notably
different reconstruction of the CO₂ record by Rothman (2002),
shown in Figure 9b, also offers no suggestion of significant correlation.
CO₂ is a particularly ridiculous choice for a ‘pollutant.’ Its primary role is as a fertiliser for plant life. Currently, almost all plants
are starved of CO₂. Moreover, if we were to remove a bit morethan 60% of current CO₂, the consequences would be dire: namely death by starvation for all animal life. It would not likely leadto a particularly cold world since such a reduction would only
amount to a couple of percent change in the radiative budget.
After all, a 30% reduction of solar radiation about 2.5 billion years
ago did not lead to an Earth much colder than it is today, as we
earlier noted in connection with the Early Faint Sun Paradox.

7. Impacts
The preceding discussion was restricted to physics. It did not
address the issue of so-called ‘impacts’, whereby any observedchange in anything is immediately claimed as evidence for the
impact of CO₂. A typical example from the Boston Globe of April
19, 2022 follows:
Despite increasingly urgent international warnings andan onslaught of catastrophic wildfires and weather linked
to global warming, fewer Massachusetts residents see theclimate crisis as a very serious concern than they did three
years ago, according to a new poll.
The inevitable conclusion is that we should be decarbonising.
Such ridiculous leaps of irrational inference go well beyond absurdity, although the common sense of Massachusetts residents
is heartening. Unfortunately, the understandable temptationof sceptics to point out that the alleged changes are misrepre12

6000

4000
22
2000
17
0

12

5

(b)

4

3
22
2

1
600

Average global temperature (°C)

(a)

17

500

400

300
200
Million years ago

100

0

Average global temperature (°C)

Temperature
Carbon dioxide

Atmospheric CO₂ (parts per million)

Temperature reconstruction after CR
Scotese. CO₂ reconstructions after(a) RA Berner and Z Kothavala (2001)
and (b) Rothman (2002). Note thatat time of publication the scale on
Fig. 9a was erroneous, and has now
been corrected.

8000

pCO₂(t)/pCO₂(0)Figure 9: Paleoclimate
reconstructions oftemperature and CO₂.

12sented (wildfires have decreased greatly over the past couple ofgenerations), leaves in place the bizarre suggestion that had theclaimed changes been real, they implied the need for decarbonisation.

8. Where does this leave us?
This all leaves us with a quasi-religious movement predicated on
an absurd ‘scientific’ narrative. The policies invoked on behalf of
this movement have led to the US hobbling its energy system (aprocess that has played a prominent role in causing current inflation), while lifting sanctions for Russia’s Nordstream 2 pipeline,
which was designed to bypass the existing pipeline through the
Ukraine used to supply Germany. It has caused much of the European Union to ban exploitation of shale gas and other sourcesof fossil fuel, thus leaving it with much higher energy costs, increased energy poverty, and dependence on Russia, thus markedly reducing its ability to oppose Mr Putin’s aggressions.
Unless we wake up to the absurdity of the motivating narra13

tive, this is likely only to be the beginning of the disasters that will
follow from the current irrational demonization of CO₂. Changing course will be far from a simple task. As President Eisenhower
noted in his farewell address in 1961:
The prospect of domination of the nation’s scholars by Federal
employment, project allocations, and the power of money isever present and is gravely to be regarded.
Yet, in holding scientific research and discovery in respect, as
we should, we must also be alert to the equal and opposite
danger that public policy could itself become the captive of ascientific-technological elite.
As described in detail in Lindzen (2008, 2012), the US government committed itself to the current narrative by the early
1990s and greatly increased funding as a result. Moreover, given
the size of the energy sector, any attempt to rebuild it, however
unnecessarily and ineffectively, presents immense opportunities
for huge short-term profits – opportunities that are obviously
tempting and strongly defended. Atop all of this, has been theconstant Goebellian repetition by the media of climate alarm.
And, this alarm is accompanied by so-called ‘solutions’ that deal
with something, namely decarbonisation, that is, in fact, largely
irrelevant to climate change, while imposing great and pointlesspain.
It is essential – to western civilization itself – that the harm
associated with this totally unwarranted alarm be ended, however difficult the task.

Acknowledgements
No support for the preparation of this paper has been provided
by any agency or party – public or private. However, useful suggestions by William Happer, Simon Scott and William Ponton are
gratefully acknowledged.

14

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31. D.H. Rothman, Atmospheric carbon dioxide levels for thelast 500 million years, PNAS 99(7) (2002), 4167–4171, https://doi.
org/10.1073/pnas.022055499 (2002).
32. C. Sagan and G. Mullen. Earth and Mars: evolution of atmospheres and surface temperatures. Science 177(4043) (1972), 52–56.
33. N. Shackleton, A. Boersma, The climate of the Eocene ocean.
Journal of the Geological Society of London 138 (1981), 153–157.

16

Comment from Nic Lewis
My overall view of this essay is that it makes many good points
and will help convey key aspects of the Earth’s climate system
to non-expert readers, although some may find it challenging tounderstand in one or two places. While, in my view, its downplaying of the role of changes in CO2, as amplified by feedbacks, may
go a bit too far, that does not negate the main thrust of the essay.
Taking the sections of the essay in turn, Section 1, The Popular Narrative, is mainly uncontentious, although the values forthe radiative effect of a doubling of CO2 concentration and theresulting no-feedback global warming are slightly low relative tocurrent widely-accepted estimates.
Regarding the effects of feedbacks, the view that atmospheric water vapour will increase with global warming, causing
a positive feedback, amplifying surface warming, since water vapour is itself a greenhouse gas (albeit one whose concentration
is temperature-controlled), is long established. It seems quite difficult to argue against, since the maximum water vapour that air
can hold increases strongly with temperature, and there is a lackof good evidence that humidity in the atmosphere as a proportion of that maximum falls strongly with temperature. However,a reduction in the adiabatic lapse rate with increasing water vapour concentration partially counteracts the water vapour feedback, with (in the absence of other feedbacks) the net effect ofthese two linked factors equating to a 50% or so increase in thebasic warming from a rise in CO2 concentration.
On the other hand, whether cloud changes amplify warming, as IPCC assesses1 they do (and the vast majority of climate
scientists appear to believe so), or attenuate it, remains uncertain. Bjorn Stevens – arguably the most impressive and influentialof the current generation of climate scientists, and a very central,senior figure in the ‘IPCC consensus community’ – has recently argued against cloud feedback being positive, claiming that clouds
mute rather than amplify climate sensitivity.2 The remaining feedback assessed by the IPCC to be significant is a positive feedback
due to the albedo of the surface decreasing as high latitude sea
ice and snow cover reducing when the Earth warms. However, a
recent paper3 (whose lead author is a very experienced cloud expert), finds that the changes in surface reflection involved haveno statistically significant impact on radiation trends at the topof the atmosphere, which are the primary measure of feedback
strength. Taken together, this evidence would suggest 1.5°C to
2°C long-term global warming from a doubling of CO2 concentration (‘climate sensitivity’) – around half that implied by the IPCC’s
assessment of feedbacks and barely a third of that implied by anumber of the latest global climate models (GCMs) that are used
for climate change projections.
Section 2 of Lindzen’s essay makes the point that changes
in mean temperature that have occurred over the last century or
so, thought by most climate scientists to be likely almost entirely
17due to anthropogenic changes in greenhouse gases and otheratmospheric constituents, are trivial compared to those due toseasonal and other natural fluctuations, which humans are used
to coping with. Accordingly, claimed existential threats are illusory. These are valid and very important points. They are bolsteredby the fact that evidence for increased occurrence of weather
extremes (such as droughts, floods, hurricanes, heat waves, etc.)
is weak or non-existent, except for there being more high-temperature periods – as one would expect when the average temperature is higher. Similarly, claimed adverse effects of global
warming to date often turn out to be illusory. Wildfires have notincreased,45 the polar bear population has not decreased,6 coral
reefs have survived (the Great Barrier Reef has record coral cover7), the land area of low lying atoll islands has increased.8
Section 3 is uncontentious, but its point that global warming
or cooling mainly involves changes in the polar–equatorial temperature differential, with changes in equatorial temperatures
being far smaller, is important. It implies that greenhouse gas
warming will be much greater in cooler, higher latitudes (wherewarming has some benefits) than in the tropics.
Section 4 ‘What determines the tropics-pole temperature
difference?’ discusses difficult scientific issues that are not fully
understood. It is well established that, as Lindzen implies, poleward heat transport from the tropics is mainly by transient, unstable baroclinic eddies. However, it is less clear what controls
the magnitude of the heat transported poleward, and hence thetropical–polar temperature differential and changes in it. A 2019
paper9 argues that it can be best understood from an energetic
perspective (balancing latitudinally-varying radiative surpluses
and deficits), and that this can explain why temperature changes
are much greater at high latitudes than in the tropics. That explanation, if correct, does appear to me to be consistent with thegreenhouse effects of changing CO2 concentration. However, as
Lindzen says, the changing magnitude of Arctic temperature inversions also appears to be an important influence on polar amplification of tropical warming; this may slightly increase global
warming. Towards Antarctica, however, strong heat absorption
by the Southern Ocean is thought to substantially delay warming amplification.
Although many scientists have questioned Lindzen’s contention, there does appear to be considerable evidence for thetropical ‘iris effect‘ discussed in Section 5, although it remains unclear how strong this effect is.
The lack of correlation between CO2 concentration and deep
paleoclimate temperatures shown in Section 6 is striking. Overgeologically-recent glacial cycles, where CO2 concentration andtemperature do co-vary, there is, however, a complicating factor
in determining causation. A rise in temperature is expected tocause a rise in CO2 (which is less soluble in a warmer ocean), so atiming lag of CO2 change on temperature change does not ruleout a causal role for CO2 in climate change.
18

The points Lindzen makes in the final section of his essay
concerning climate change related policies and the harm theyand the underlying alarmist narrative are causing appear fully
justified. Even accepting that reducing net anthropogenic CO2
emissions, ultimately to a very low level, will be necessary to
prevent global temperatures continuously increasing, current
policies designed to achieve this at breakneck speed seem likely
to cause considerably more harm than good. Indeed, rapid CO2
emission reductions in the UK will have a negligible impact on
global warming, and those by all other Western nations will have
only a minor impact. Such reductions will thus serve mainly tomake their elites feel virtuous at the expense of their populations
as a whole, unless other nations respond by cutting their emissions as deeply and as fast – which appears rather unlikely.
Nicholas Lewis is an independent climate scientist whose work focuses on estimation of climate sensitivity and improving related statistical methodology. He is sole or lead author of ten peer reviewed
publications in this area.

Notes

1. Forster P et al., 2021, The Earth’s energy budget, climate feedbacks, and climate sensitivity. In: Climate Change 2021: The PhysicalScience Basis. Contribution of Working Group I to the Sixth Assessment
Report of the Intergovernmental Panel on Climate Change. Cambridge
University Press.
2. Stevens B (with Kluft L), 2022, Clouds Help Moderate Greenhouse Warming, CFMIP_2022 Conference Presentation. https://drive.google.com/drive/folders/1MxQptblqckxLtVbLeJ9ZIRbwURS
ob9i1
3. Stephens GL et al., 2022, The changing nature of Earth’s reflected sunlight. Proceedings of the Royal Society A. 478(2263):20220053.
4. Liu, Pengfei, et al. ‘Improved estimates of preindustrial biomassburning reduce the magnitude of aerosol climate forcing in theSouthern Hemisphere‘. Science Advances 7.22 (2021).
5. Marlon, Jennifer R., et al. “Climate and human influences on
global biomass burning over the past two millennia.” Nature Geoscience 1.10 (2008): 697-702. https://doi.org/10.1038/ngeo313
6. Crockford, S, The Polar Bear Catastrophe That Never Happened,2019,
https://www.amazon.com/Polar-Bear-Catastrophe-NeverHappened/dp/0993119085
7. Australian Institute of Marine Science, 2022, Annual Summary
Report of Coral Reef Condition 2021/22. https://www.aims.gov.au/monitoring-great-barrier-reef/gbr-condition-summary-2021-22
8. Duvet, KE, 2019, A global assessment of atoll island planformchanges over the past decades. WIREs Climate Change https://doi.
org/10.1002/wcc.557
9. Armour KC et al., 2019, Meridional atmospheric heat transport
constrained by energetics and mediated by large-scale diffusion.
Journal of Climate, 32(12), pp. 3655–3680.

19

Response by Richard Lindzen
I wish to thank Nic Lewis for his careful reading of my paper. At
the very least, he makes it evident where I have not been adequately clear. This is, perhaps, to be expected when one tries tosummarize such a complex subject in about 14 pages.
Having said that, Lewis is guilty of using what I referred toas the one-dimensional picture when he discusses the so-called
water vapor feedback. In this picture, there is one value of both
humidity and relative humidity. However, as I and colleagues
have long noted (Lindzen, et al, 2001 and references therein), humidity varies greatly in space and time. Moreover, where there
are high cirrus clouds, the cirrus determine the effective emission level, and the cirrus also vary in their spatial coverage. As aresult, there really is no meaning to the water vapor feedback as
an isolated process; instead one must look at a generalized longwave feedback. This appears to be negative (Lindzen, et al, 2001,
Lindzen and Choi, 2021, Trenberth and Fasullo, 2009).
Without the alleged water vapor feedback, it is difficult toaccount for even the sensitivity that Lewis suggests. Indeed, withhigh sensitivities, models have generally had to cancel alleged
warming with counteracting sulphate aerosols. As I and others
have noted, many of these fudges involved more sulphate aerosols than are now regarded as possible. I discuss this in detailin Lindzen (2020). I would also mention that the claim by Lewis
that a roughly 2% contribution from doubling CO₂ leading to awarming of about 1°C being a slight underestimate of the resulting warming is open to significant doubt. As shown by van
Wijngaarden and Happer (2022), a careful line-by-line calculationsuggests that the contribution is about 1.1% rather than 2%. As
I also note in the current paper, the climate science community was quite small prior to the initiation of the global warming
alarm, which led to a massive increase in the number of individuals identifying as climate scientists. It is somewhat bemusing tohear Nic Lewis speak of the ‘vast majority of climate scientists.’
I would add that the notion that any adverse change in anything implies a role for CO₂ is also unjustified. In addition, I would
remind the reader that my Section 2 also shows that the globally
averaged temperature anomaly bears comparatively little relation to what is going on at any particular station.
Lewis seems to remain attached to the notion of polar amplification (i.e. that changes at the pole are a direct consequenceof changes at the equator). As far as I can tell, this is a misreadingof how the climate system works – at least for the major climatechanges referred to in my paper. With respect to Lewis’ remarks
on my Section 4, the processes associated with greenhouse response are largely confined to the tropics. The processes leading
to changes in the tropics-to-pole temperature difference are associated with changes in the poleward heat flux out of the tropics. The fact that tropical temperatures remain minimally alteredby changing heat fluxes out of the tropics strongly points to neg20

ative feedbacks in the tropics. It should be added that althoughchanges in the tropic-to-pole temperature difference characterize major climate changes, even the present climate involves aplethora of different regimes, which current models fail to accurately account for.
Lewis seems to ignore the fact that heat transport due toinstabilities acts to bring the system to a state that is neutral
with respect to the instability. As I note, this state is calculable(R.S. Lindzen and B. Farrell, 1980, Stone, 1978, Jansen and Ferrari,2013), and provides important insights into the observed tropicto-pole differences.
When one notes that during the glaciation cycles, changes
in temperature precede changes in CO₂, one is talking about theorder of a thousand years in the case of glaciation and a hundredyears in the case of deglaciation. The case for such a reverse causality becomes quite slim. Moreover, should there be such longlags, it would be problematic to deduce anything from the slighttemperature increase over only about 60 years (i.e., the period
during which forcing due to increased CO₂ was significant). But,
more to the point, the orbital forcing suggested by Milankovitch
is almost two orders of magnitude greater than what could be attributed to CO₂ and provides the proper time dependence.
Lewis is right in noting that proposed policies are harmful regardless of what one believes about the nature of climatechange. My point is simply that this is doubly true if the underlying premise concerning the role of greenhouse gases is wrong.
My paper represents my assessment of how the climate system actually works. It is the result of almost 60 years of work on
the behavior of the physics and dynamics of the atmosphere, andthe evolution of my thinking since Lindzen (1993). Of course, likeall of science, it is unlikely to represent the final word on the subject. However, I am reasonably confident that the current popularnarrative is largely incorrect. The notion that the science is ‘settled’ is pretty implausible in either case.

References
1. M. Jansen, R. Ferarri, equilibration of an atmosphere by adiabatic eddy ﬂuxes. J. Atmos. Sci. (2013). https://doi.org/10.1175/
JAS-D-13-013.1.
2. R.S. Lindzen and B. Farrell (1980). The role of polar regions in
global climate, and the parameterization of global heat transport.
Mon. Wea. Rev., 108, 2064-2079.
3. R.S. Lindzen (1993) Climate dynamics and global change. Ann.
Rev. Fl. Mech., 26, 353-378.
4. R.S. Lindzen, M.-D. Chou, A.Y. Hou, Does the Earth have an adaptive infrared iris? Bull. Am. Meteorol. Soc. 82(3), 417–432 (2001).
5. Lindzen, R.S. (2020) On Climate Sensitivity, http://co2coalition.
org/wp-content/uploads/2020/04/Climate-Sensitivity-06.07.20.
pdf.

21

6. R.S. Lindzen and Y.-S. Choi: The Iris Effect: a review, Asia-Pacific Journal of Atmospheric Sciences, https://doi.org/10.1007/s13143021-00238-1 (2021).
7. Stone, P. H., 1978: Baroclinic adjustment. J. Atmos. Sci., 35, 561571.
8. Trenberth, K. E. and J.T. Fasullo (2009), Global warming due toincreasing absorbed solar radiation. Geophys. Res. Let., 36, L07706.
9. W.A. van Wigngaarden and W. Happer (2022) https://co2coalition.org/wp-content/uploads/2022/03/Infrared-Forcingby-Greenhouse-Gases-2019-Revised-3-7-2022.pdf.

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